<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>https://codepen.io/prvnbist/pen/gKParr</title>
	<style type="text/css">
      body {
        display: flex;
        justify-content: center;
        align-items: center;
        min-height: 100vh;
        background: white;
      }

      .button {
        position: relative;
        appearance: none;
        background: #f72359;
        padding: 1em 2em;
        border: none;
        color: white;
        font-size: 1.2em;
        cursor: pointer;
        outline: none;
        overflow: hidden;
        border-radius: 100px;

        span {
          position: relative;
          pointer-events: none;
        }

        &::before {
          --size: 0;

          content: '';
          position: absolute;
          left: var(--x);
          top: var(--y);
          width: var(--size);
          height: var(--size);
          background: radial-gradient(circle closest-side, #4405f7, transparent);
          transform: translate(-50%, -50%);
          transition: width .2s ease, height .2s ease;
        }

        &:hover::before {
          --size: 400px;
        }
      }
    </style>
</head>
<body type="pug">
<button class="button">
    <span>Hover me I'm awesome</span>
</button>
<script>
    document.querySelector('.button').onmousemove = (e) => {

        const x = e.pageX - e.target.offsetLeft
        const y = e.pageY - e.target.offsetTop

        e.target.style.setProperty('--x', `${ x }px`)
        e.target.style.setProperty('--y', `${ y }px`)

    }
</script>
</body>
</html>